THOMAS: INFECTION OF APIUM GRAVEOLENS 19 
that the time* required for the first appearance of the spots was 
practically identical for the etiolated and control plants. 
A third set of plants was kept in thedark room for five days, 
beginning on the thirteenth day after inoculation, at which time 
the spots were just beginning to appear. This dark room was 
provided with a ventilator which caused a continuous circulation: 
of air from the greenhouse in which the control plants were kept 
thus providing similar atmospheric conditions for the two sets of 
plants. This experiment was performed during the warm weather 
of July, and as a result the plants kept in the dark room lost several 
of the older leaves. Although the total counts of infections could 
not be obtained it is scarcely to be expected that the number of 
spots would be altered by this treatment. 
TABLE X 
EFFECT ON SIZE OF SPOT OF ETIOLATION AT DIFFERENT TIMES RELATIVE TO 
INOCULATION 
a. Plants kept in dark room nine days preceding inoculation 
Etiolated plants Control plants 
Plant No. . 
Average size spot No. of leaves Average size spot | No. of leaves 
I 1.62 5 be OF 
2 5f 5 1.16 | 9 
3 1.37 4 0.91 | 4 
4 1.54 3 0.95 8 
5 1.45 3 0.94 4 
b. Plants kept in the dark room from the fifteenth to the eighteenth day after inoculation 
I | 2.08 = t.27 2 
2 1.87 2 1.51 4 
3 1.50 2 1.07 i. 
4 1.80 I 1.81 3 
5 | ia eo 2 1.45 3 
6 | 1.78 3 1.33 3 
This seemed to be borne out by counts from the individual 
leaves. The effect upon the size of the spot produced by etiolation 
at this time was readily demonstrable. Taste X shows the 
increase in diameter of spots upon plants etiolated both before and 
after inoculation. Except for an occasional leaf (nine altogether) 
+E yemniie found (12) that Puccinia coronifera on oats was almost completely 
arrested in its progress during the time in which inoculated plants were kept in the 
dark roo! 
